Mercy’s Valkyrie is no longer for Rezzing. It’s for healing your whole team while being hard to hit. Many Mercy players claim that it’s an ultimate that has no impact, which is completely false. It’s very effective for pushing forward with your team, or for helping your team survive the enemy engaging you
Think of it like Orisa’s supercharger and Zen’s Transcendence in 1. (weakened versions of them of course, because it’s a 2 in 1 ability.